Historically, dowel-mill head assembly-assemblies have relied on two means of lubrication; either A) Bearing-grease, usually providing lubrication for ball-bearings; or B) Lubricating-oil which is applied and distributed through the assembly, usually for lubrication of roller-bearings. Each of these types of bearing-lubrication has associated with it its own unique set of drawbacks.
For example, the use of grease as a lubricant usually leads to: A) higher operating temperatures, (since no mechanism exists for heat-dissipation from the head, except for convection-cooling with the ambient-air), and B) lower operating assembly rotation speed. Lower operating-assembly rotational-speeds not only restrict product output-levels but also functions to severely-limit the quality of the finished milled-product. Higher operating temperature-levels will naturally lead to increased stress on assembly-parts and which in turn leads to increased maintenance-requirements.
In comparison to grease, use of lubricating-oil as a bearing-lubricant in a dowel-mill head assembly provides reduced operating temperature-levels, due to the improved-ability of the lubricating oil-stream (stream of lubrication oil) to carry heat away from the head, (as compared to the air-cooling mode of heat-transfer associated with a grease-lubricated system). As a consequence, operating-assembly rotational-speeds can be increased greatly, with several beneficial-results, including; A) greater product output, B) better surface-finish quality on the finished wood-dowels, and C) reduced equipment maintenance-requirements. A lubricating-oil system, however, places more stringent performance requirements on the sealing-system in the dowel-mill head assembly, due to; A) the much-lower viscosity of the lubrication oil compared to grease, and B) the greatly-increased rotational-speeds allowed by such a system.
The sealing-system commonly found in earlier dowel-mill head assembly-assemblies which utilize lubricating-oil as a bearing-lubricant, typically achieve lubrication oil-retention within the head through the use of various-types of “contacting” oil-seals. A “contacting”-seal (contact-type) is defined as type of seal which forms a barrier to lubricant-loss at each rotating-interface through use of a flexible-type lip, which is positioned to make light-contact with a particular rotating part of the head, thus forming the required lubricant-seal. The seal-lip typically utilizes a flexible, heat & petroleum-resistant material such as Neoprene. Although this type of seal can be effective in its role, there are multiple functional-limitations associated with this type of seal including: A) Wear of the seal-lip, and B) Heat-generation occurring as a result of rubbing-friction between the lip and the rotating seal-surface. As a result, “contacting”-seals are considered to be consumable-entities, requiring periodic-replacement, typically after every 500-600 hours of operation. Seal-replacement, in the case of a dowel-mill head assembly, requires that each time the head be removed from the machine, disassembled, cleaned, and rebuilt, using new seals. This procedure can lead to large yearly maintenance-costs, (in both labor & materials), in addition to many hours each year where the unit is out of service, (downtime).
This invention discloses a specific mill head assembly, utilizing centrifugal hydrodynamic force and other properties of fluid dynamics, which directs lubricant flow and retains lubricant without the need for a replaceable (contact-type) seal.